I’ll start by saying that not all ghettos are populated by blacks. The word ghetto itself comes from an Italian term for the area of the town to which Jews are restricted (ethnic Jews are not black). In the United States, the term ghetto has come to mean an urban or suburban area that is poor, a.k.a. low-income, and racially homogenous.
It is true that historically, before the large-scale arrival of other racial groups, American ghettos were populated by blacks. The main reason for this is the Great Migration of African Americans away from the South, along with racist housing policies and possibly some self-segregation.
Before 1910, 90% of America’s black population lived in the South, where blacks had been enslaved, and remained for social and economic reasons. Starting in the 1910s and especially in the 1930s, Southern blacks began moving in large numbers to Northern industrial cities. They wanted to escape racism and violence, and saw opportunity in growing Northern industry.
By 1970, only 50% of black Americans lived in the South. The rest had primary moved to inner-city industrial areas in big cities like Chicago, New York and Detroit. The North certainly afforded blacks more opportunities than the South, but racism was still pervasive. White Americans for the most part did not want black neighbors. Racist housing and renting policies meant that blacks were only able to rent or buy housing in certain parts of town, typically the dirty industrial areas. In addition, when numerous blacks moved into white neighborhoods, whites would quickly relocate out of fear of a potential rise in property crime, rape, drugs and violence that was attributed to neighborhoods with large black populations. This resulted in most Northern cities having a black “ghetto” in the traditional sense – a part of town to which blacks were restricted.
In the 1970s and the years that followed, Northern industry began to decline. White industrial workers generally had no problem moving out to the suburbs, or taking out a loan to start small businesses. Over time, most of the traditional white ghettos managed to fade away. The poor black ghettos, however, remained—it was harder for blacks to get loans and hew housing. In addition to outright racism, white suburbs were not accommodating to black culture. Poor urban blacks were stuck and often had to resort to extralegal means of making money—often with drugs—perpetuating the negative stereotypes that blocked them from escaping poverty.
After several decades, things are slowly beginning to change. It’s still true that the poorest parts of American cities are often inhabited by blacks. However, the term “ghetto” has been appropriated into a totally new cultural phenomenon, representing urban black culture. People of all races and incomes are often seen emulating ghetto culture. For many black Americans it is a rare source of pride. This leads to a complicated situation—African American communities are eager to rise out of poverty, but reluctant to get rid of ghetto culture, which is central to many blacks’ identity.
What about non-black ghettos?
It’s a bit of a different story. It’s easy to broadly blame it all on racism, but the real story is much more nuanced. Most Asians and Hispanics, unlike blacks, are recently immigrated. Asians and Hispanics did face racial discrimination in housing, which is how “Chinatowns” first appeared. However, most Asian and Hispanic immigrants arrived in the United States after such overt racism had largely subsided.
In the case of Hispanic or Latin ghettos, they are actually a legacy of the white-black racist struggle. Affordable housing left behind by whites who fled the decline of industry was taken up by Hispanic immigrants. Blacks who did manage to move out to the suburbs also left behind affordable urban housing, which mostly Hispanics took up. Subsequent generations of Hispanic immigrants often settled in these newly-Hispanic ghettos, reinforcing the racial divide. They did this for several reasons: affordable housing, family or friends, and the Spanish-English language barrier.
Asian ghettos in the US are now rare, mostly found on the West Coast. Usually these areas are inhabited by Filipinos, Vietnamese, and people from other lower-income East Asian countries. This is because other Asian nationalities either came to the US with advanced skills (e.g. Koreans, Indians), or had gradually integrated and shifted out of ghettos over the generations (many Chinese, Japanese). The reasons for these Asian ghettos existing are largely the same as for Hispanics—self-segregatio
Outright racism is much less of a factor for these groups than it was for blacks, since their arrival came mostly after the 1970s. Hispanic and Asian Americans are more economically successful and less racially segregated than African Americans.